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SGUL - Physiology 2 > Chemical Senses > Flashcards

Chemical Senses Flashcards

1
Q

List the chemical senses in the body

A
  • Taste
  • Smell
  • Chemical irritants
  • CO2/O2 levels
  • Acidity
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2
Q

How can our taste be innate? (In born)

A
  • Some of our taste preferences are inborn
  • Humans innately enjoy sweet flavours and avoid bitter flavours, this is evolutionary ancient
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3
Q

How can our taste be learned?

A
  • Our experience can also modify our innate preferences
  • Humans can learn to tolerate or enjoy the bitterness of some substances
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4
Q

How can we perceive flavour?

A

Via 3 different systems
- Smell
- Touch: Texture, temperature
- Taste: Sweet, Bitter, Sour, Salt, Umami

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5
Q

Define taste

A
  • Primarily a function to the tongue
  • However other areas of the mouth such as the mouth, throat and nasal passages also have important roles in taste
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6
Q

What are the organs of taste?

A
  • Palate: Roof of mouth separating oral and nasal cavities, taste buds present in palate
  • Epiglottis: Leaf shaped cartilage covering laryngeal inlet, taste buds present here
  • Pharynx and Nasal cavity: Odoura can pass via the pharynx, to the nasal cavity to be detected by olfactory receptors
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7
Q

Describe the features of the tongue

A

The surface of the tongue contain papillae
- Ridge shaped (foliate)
- Pimple shaped (vollate)
- Mushroom shaped (fungiform)

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8
Q

What does the papillae also contain?

A
  • Contains taste receptors cells
  • These taste buds are surrounded by basal cells and gustatory afferent axons
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9
Q

Describe taste receptor cells

A
  • Express different types of taste receptors
  • Most taste receptor cells respond primarily to one of the 5 basic tastes
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10
Q

How does taste receptor cells work?

A
  • Three taste receptor cells sequentially exposed to Salt, bitter, sour and sweet stimuli
  • Membrane potential recorded
  • Taste receptors cells display different sensitivities
  • Taste receptor cells form synapses with gustatory afferent axons to transmit this gustatory information
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11
Q

Name the 2 mechanisms for taste transduction

A
  • Saltines
  • Sourness
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12
Q

Briefly describe saltiness

A

The prototypical salty chemical is table salt (NaCl)
- Taste of salt is mostly the taste of the cation sodium (Na+)

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13
Q

How does Saltiness act as a transduction mechanism?

A
  • Na+ passes through Na+ selective channels down its concentration gradient
  • This depolarises the taste cell, activating voltage gated calcium channels
  • Vesicular release of neurotransmitters is elicited and gustatory afferent activated
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14
Q

Why are special Na+ selective channels used?

A
  • Used to detect low concentrations of salt
  • Insensitive to voltage and generally stays open
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15
Q

Briefly describe sourness

A

Protons (H+) are the determinants of acidity and sourness

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16
Q

How does sourness act as a transduction mechanism?

A
  • H+ can affect sensitive taste receptors in several ways
  • However it’s likely that H+ can pass through proton channels and bind to and block K+ selective channels
  • This leads to depolarisation of the taste cell activating VGSC & VGCCs
  • Vesicular release of neurotransmitters is elicited and gustatory afferent activated
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17
Q

Name the different mechanisms of taste transduction (GPCR mechanisms via T1 and T2 taste receptors)

A

Bitterness
Sweetness
Umami

18
Q

Briefly describe taste receptor proteins (T1R and T2R)

A

Transduction mechanisms underlying bitter, sweet and umami tastes rely on two families of related taste receptor proteins: T1Rs and T2Rs

19
Q

Describe how taste receptor proteins work

A

T1R and T2Rs are G protein coupled receptors and are Gq linked
1. Bitter substances are detected by approximately 25 T2Rs
2. Sweet substances are detected by one receptor (T1R2 & T1R3 proteins)
3. Umami substances are detected by one receptor (T1R1 and T1R3 proteins)

20
Q

What is the bitterness transduction mechanism? (PART 1)

A
  • Bitter tastings binds to T2R which is a G protein Gq
  • This stimulates the enzyme phospholipids C (PLC) leading to the production of inositol triphosphate (IP3)
21
Q

What is the bitterness transduction mechanism? (PART 2)

A
  • IP3 intracellularly activates a special type of Na+ ion channel and releases Ca2+ from intracellular storage sites
  • Both these actions depolarise the taste cell – release of ATP is elicited, and gustatory afferents are activated
22
Q

What is the sweetness transduction mechanism?

A
  • Sweet tastants binds to diner receptor formed T1R2 and T1R3 which is coupled by G protein Gq linked
  • The same signal transduction mechanism as bitterness occurs
23
Q

Why do we not get confused between bitter and sweet tastes?

A
  • Taste cells express either bitter or sweet receptors
  • Not both
  • This causes the bitter and sweet taste cells to connect to different gustatory axons
24
Q

What is the Umami taste transduction mechanism?

A
  • Umami tastants bind to diner receptor formed from T1R1 and T1R3 which is coupled to the G protein Gq
  • The same signal transduction mechanism as bitterness and sweetness occurs
  • Shares T1R3 protein with sweetness
  • T1R subunit determines specificity to umami
25
Q

Why do we not get confused between bitter, sweet and umami tastes?

A
  • Taste cells express either bitter, sweet or umami receptors
  • Therefore bitter, sweet and umami taste cells connect to different gustatory axons
26
Q

What is the flow of taste information to the CNS?

A
  • Taste cells -> Gustatory axons -> Gustatory nucleus (Medulla) -> Ventral posterior medial nucleus (Thalamus) -> Gustatory cortex
27
Q

Which three cranial nerves carry gustatory axons and bring taste information to the brain?

A

Facial Nerve
Glossopharyngeal Nerve
Vagus Nerve

28
Q

How can our smell be innate?

A

Some of our smell preferences can be inborn

29
Q

How can smell be learned?

A

Experience can strongly modify our innate preferences

30
Q

What are pheromones?

A

An Olfactory stimuli used for chemical communication between individuals

31
Q

Give some examples of where pheromones are used

A

In some animals, Phermomes are important signals for:
- Reproductive behaviour
- Marking territories
- Indicating Aggression/Submission

32
Q

Where can Olfactory receptor cells be found?

A

At the site of transduction

33
Q

What is the function of Olfactory receptor cells?

A
  • Function is to produce mucus
  • Odorants dissolve in mucus layer before contacting cilia of olfactory receptor cells
34
Q

What does the olfactory receptor cells do in the Basel cells?

A
  • Immature olfactory receptor cells are able to differentiate into mature olfactory receptor cells
  • Olfactory receptor cells continuously grow, degenerate and regenerate
35
Q

What is the Olfactory transduction mechanism?

A
  • Odorant molecules bind to odorant receptor proteins on the cilia
  • Olfactory-specific G-protein (Golf) is activated
  • Adenylyl cyclase activation increases cAMP formation
  • cAMP-activated channels open, allowing Na+ and Ca2+ influx
  • Ca2+ activated chloride channels open enabling Cl- efflux
  • Causes membrane depolarisation of the olfactory neuron
36
Q

What is the flow of smell information to the CNS?

A
  • Olfactory receptor cells send axons into the olfactory bulb
  • Olfactory receptor cells expressing the same receptor proteins project to the same glomeruli in the olfactory bulb
  • Signals are relayed in the glomeruli and transmitted to higher regions of the brain
37
Q

What happens in population coding?

A

The response of a large number of broadly tuned neurons are used to specify the properties of particular stimuli

38
Q

How can the brain distinguish between specific tastes and smells in Gustation and Olfaction stimuli? (Population coding)

A
  • Gastatory and olfactory receptor cells may express only one specific receptor protein
  • However Gustatory and Olfactory axons along with the neurons they activate in the brain, respond more broadly
  • Only with large population of neurons, with different response patterns, can the brain distinguish between specific tastes and smells
39
Q

Give an example of population coding for olfaction (PART 1)

A
  • Olfactory receptor cells express a single olfactory receptor protein – each can respond to different odours with differing preferences
  • When presented with a citrus smell, none of the three receptor cells can individually distinguish it from the other odours
40
Q

Give an example of population coding for olfaction (PART 2)

A
  • However, the brain can distinguish the citrus smell through the combination of responses from all three cells
  • It is estimated that humans can discriminate at least one trillion different combinations of odour stimuli

SGUL - Physiology 2 (37 decks)

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